/**
 * Logback: the reliable, generic, fast and flexible logging framework.
 * Copyright (C) 1999-2013, QOS.ch. All rights reserved.
 *
 * This program and the accompanying materials are dual-licensed under
 * either the terms of the Eclipse Public License v1.0 as published by
 * the Eclipse Foundation
 *
 *   or (per the licensee's choosing)
 *
 * under the terms of the GNU Lesser General Public License version 2.1
 * as published by the Free Software Foundation.
 */
package ch.qos.logback.core.pattern;

/**
 * A minimal converter which sets up the general interface for derived classes.
 * It also implements the functionality to chain converters in a linked list.
 *
 * @author ceki
 */
abstract public class Converter<E> {

  Converter<E> next;

  /**
   * The convert method is responsible for extracting data from the event and
   * storing it for later use by the write method.
   *
   * @param event the log event
   * @return the string conversion
   */
  public abstract String convert(E event);

  /**
   * In its simplest incarnation, a convert simply appends the data extracted from
   * the event to the buffer passed as parameter.
   *
   * @param buf The input buffer where data is appended
   * @param event The event from where data is extracted
   */
  public void write(StringBuilder buf, E event) {
    buf.append(convert(event));
  }

  public final void setNext(Converter<E> next) {
    if (this.next != null) {
      throw  new IllegalStateException("Next converter has been already set");
    }
    this.next = next;
  }

  public final Converter<E> getNext() {
    return next;
  }
}
